Method for combining components made of different materials

ABSTRACT

A method for combining two components together includes the following steps: a) surface treating the two components; b) placing them within a heating apparatus while they contact with each other, a force being applied to the two components to push then against each other on the contacting surfaces thereof; c) heating the two components to a predetermined temperature which is hold for a predetermined period time to cause the two components to diffuse at the contacting interface to thereby combine the two components together; d) cooling the combined two components and taking them out of the heating apparatus.

FIELD OF THE INVENTION

The present invention relates generally to a method for combining components made of different materials, and more particularly to a method for combining components made of different metals.

DESCRIPTION OF RELATED ART

Advances in microelectronics technology have resulted in electronic devices which process signals and data at unprecedented high speeds. During operation of many contemporary electronic devices such as central processing units (CPUs), large amounts of heat are produced. The heat must be efficiently removed, to prevent the system from becoming unstable or being damaged. Heat sinks are frequently used for dissipating heat from these electronic devices.

Typical heat sinks are often integrally made by extruding aluminum (Al). However, Al has a relative low heat conductivity, i.e., 735 KJ/(M.H.K) compared with copper (Cu), i.e., 1386 KJ/(M.H.K). Thus, conventional heat sinks made by extruding Al cannot meet heat dissipating requirement of contemporary CPUs which are performing tasks faster and faster and thus generating more and more heat. Accordingly, heat sinks made by combining two components respectively made of Al and Cu have been developed.

Nowadays, two components respectively made of Al and Cu are generally combined via solding, screws, pressing and so on. However, in solding, a layer of oxide i.e., Al₂O₃, is inevitably formed at a predetermined combining surface of the component made of Al, which impacts solding effective of the two components and results in a higher thermal resistance being formed at the interface between the two components. The method of using screws employs heat conductive medium filled between the two components and combines the two components with screws. The roughness of the combining surfaces of the two components impacts the effect of combination of the two components. Furthermore, it is difficult to control twisting force of the screws to cause the two components to be tightly combined together without damaging the two components. In pressing method, a component made of Al defines a cylindric hole and the other component made of Cu has a cylindric configure. The diameter of the component made of Cu is slightly larger than that of the component made of Al. The component made of Cu is pressed into and therefore interferentially received in the hole of the component made of Al. However, the component made of Al is prone to be scraped by the component made of Cu at the hole in the pressing process, which may increase the thermal resistance between the two components.

Therefore, it is desired to design a novel method for combining two components to overcome the aforementioned problems.

SUMMARY OF INVENTION

A method for combining two combining surfaces of two components together, includes the following steps: a) surface treating the combining surfaces to reduce roughness thereof; b) placing the two components within a heating apparatus with the treated combining surfaces contacting with each other, wherein a force is applied to the components to push them against each other; c) heating the components by the heating apparatus with a predetermined temperature which is maintained for a predetermined period of time to cause atoms near the contacting interface of the two components to diffuse to each other to form a layer of alloy at the interface of the two components to thereby combine the two components together; d) cooling the combined two components and taking the combined two components out of the heating apparatus.

Other advantages and novel features of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which:

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a flow chart showing combining process for two components in accordance with a preferred embodiment of the present invention;

FIG. 2 shows the two components combined;

FIGS. 3 a-3 d respectively show thermal resistances of four sample groups A, B, C, D before and after heat treatment; and

FIG. 4 shows average thermal resistances of the four sample groups A, B, C, D before and after heat treatment.

DETAILED DESCRIPTION

FIG. 1 shows a process of a method for combining components in accordance with one embodiment of the present invention. In this embodiment, two components are used. One component is made of copper (Cu) or Cu alloy, and the other component is made of aluminum (Al) or Al alloy. Each component has a combining surface which is predetermined to connect with the other component. The method comprises the following steps:

a) surface treating the combining surfaces of the two components to reduce surface roughness thereof. In this embodiment, the surface treatment employs firstly electrolyzing or chemically polishing the combining surfaces; then removing oil or dirt on the combining surfaces by cleaning the combining surfaces with alcohol or acetone; finally removing oxidized layers on the combining surfaces by supersonic vibration to the combining surfaces;

b) placing the two treated components within an oven (not shown) with the combining surfaces thereof contacting to each other. A pair of forces is exerted on the two components to push them against each other so that a pressure stress is induced on each of the combining surfaces as shown in FIG. 2;

c) increasing the temperature of the oven in which the two components are received quickly until the temperature thereof gets to 330-420° C. and then maintaining the oven with the temperature for 1-4 hours. At this step, an alloy, such as Al₃Cu₂, is formed on the two combining surfaces of the two components due to atoms diffusion between the two components. Thus, the two components are tightly combined together with a very low thermal resistance existed at the interface thereof;

d) cooling the oven with the two combined components to the environment temperature;

e) taking the two combined components out of the oven.

In the preferred embodiment, the thermal resistance of the combined interface of the two components is subject to the following factors:

a) roughness of the combining surfaces of the two components. Lower roughness the combining surfaces of the two components have, more tighter the two components are combined together in the heat treatment process, which results in lower thermal resistance being generated at the interface between the two components.

b) forces employed to push the two components against each other. During the heat treatment process, if a predetermined compression stress is induced by applying forces on the combining surfaces of the two components, Kirkendall effect on the combining surfaces can be prevented. The Kirkendall effect is prone to generate at the interface of the two components due to atoms diffusing unequablely between the two components, which can adversely increase the thermal resistance of the interface. Generally, the stress induced by the applied forces is about 30 Mpa.

c) temperature of the heat treatment. Generally, the temperature of the heat treatment is in the range of 330-420° C., preferrably 350-370° C., at which a layer of alloy can generate at the interface between the two components. The layer of alloy with a proper thickness is capable of reducing interface thermal resistance between the two components.

d) time of the heat treatment. The layer of alloy with a thickness larger than a predetermined size may increase interface thermal resistance between the two components. Therefore, it is important to control the time of heat treatment in forming the layer of alloy so that it can have a proper thickness at the interface between the two components.

e) the percent of O₂ of the gas in the oven. In order to prevent the two components from being oxidized to form oxide which can increase thermal resistance between the two components, the percent of O2 of the gas in the oven should be reduced by such as, illing the oven with a mixture of N₂ and H₂.

For testing the embodiment of the present invention, the applicant takes an experiment as stated in the following.

The following Tab 1-1 shows the temperatures and periods of time of the oven heating four groups of samples A, B, C, D. The samples A are heated for 1 hour, the samples B are heated for 2 hours, the samples C are heated for 3 hours, and the samples D are heated for 4 hours. The data in the Tab 1-1 shows that the heat treatment temperatures of the samples are maintained substantially at 360° C. TABLE 1-1 Group of Samples Time (min) A B C D 0 355° C. 351° C. 354° C. 353° C. 30 360° C. 359° C. 359° C. 358° C. 60 360° C. 361° C. 360° C. 361° C. 90 360° C. 361° C. 362° C. 120 360° C. 360° C. 360° C. 150 360° C. 360° C. 180 360° C. 360° C. 210 360° C. 240 360° C.

FIGS. 3 a-3 d show thermal resistances of the four groups of samples A, B, C, D after heating 1, 2, 3, 4 hours respectively. Five samples are in each group of samples. FIG. 3 a shows that the thermal resistances of the samples A after heating one hour are higher than those before heat treatment. FIG. 3 b shows that the thermal resistances of some of the samples B after heating two hours are higher than those before heat treatment, while the thermal resistances of the other samples B after heating two hours are lower than those before heat treatment. FIG. 3 c shows that the thermal resistances of the samples C after heating three hours are lower than those before heat treatment. FIG. 3 d shows that the thermal resistances of the samples D after heating four hours are higher than those before heat treatment. FIG. 4 shows the average thermal resistances of the groups of samples respectively after heat treatment and before heat treatment. FIG. 4 illustrates that the average thermal resistance of the samples C, which are heated for three hours, is reduced significantly in comparison with that before heat treatment.

It is believed that the present invention and its advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention. 

1. A method for combining two components each having a predetermined combining surface, the method comprising the following steps: a) surface treating the predetermined combining surfaces to smooth them; b) placing the two components with treated combining surfaces within a heating apparatus with the treated combining surfaces contacting with each other; c) heating the two components at a predetermined temperature for a predetermined period time to cause atoms of the two components to diffuse to each other to form a layer of alloy at an interface of the two components to thereby combine the two components together; d) cooling the combined two components and taking them out of the heating apparatus.
 2. The method as described in claim 1, wherein one of the two components is made of one of Al, the other of the two components is made of Cu, and the alloy is Al₃Cu₂.
 3. The method as described in claim 2, wherein at the step b) a pair of forces is applied to the two components to induce a pressure stress at each of the combining surfaces.
 4. The method as described in claim 1, wherein the predetermined temperature is in the range of 350-420° C.
 5. The method as described in claim 4, wherein the predetermined temperature is in the range of 350-370° C.
 6. The method as described in claim 5, wherein the predetermined temperature is about 360° C.
 7. The method as described in claim 1, wherein the predetermined time is in the range of 2-3 hours.
 8. The method as described in claim 7, wherein the predetermined time is about 3 hours.
 9. The method as described in claim 1, wherein the oven is filled with a mixture of N₂ and H₂ for preventing the two component from oxidization due to heating.
 10. A product comprising first and second components made of two different metals, respectively, and an alloy of made from diffusion of the two metals and formed at an interface of the two components to combine the two components together.
 11. The product as described in claim 10, wherein one of the two components is made of Al, the other of the two components is made of Cu, and the alloy is Al₃Cu₂.
 12. A method for combining two components together which are made of copper and aluminum, respectively, comprising the following steps: a) placing the two components in an oven while the two components are subjected to a pair of forces pushing them against each other at a combining interface of the two components; b) heating the two components with a predetermined temperature for a predetermined period of time until a diffusion of the two components occurs at the combining interface to form an alloy of the two components so that the two components are combined together by the alloy; and c) cooling the combined two components.
 13. The method of claim 12 further comprising the following step before step a): surface treating the two components to reduce roughness thereof.
 14. The method of claim 13, wherein the surface treating step further comprises removing oil and oxide from the two components.
 15. The method of claim 12, wherein the forces applied on the two components induces a stress of 30 Mpa at the combining interface.
 16. The method of claim 12, wherein the two components are heated with a temperature of about 350° C.-420° C. for a period of time of about 2-3 hours.
 17. The method of claim 12, where the oven is filled with a mixture of N₂ and H₂.
 18. The method of claim 16, wherein the two components are heated with a temperature of about 360° C. for a period of time of about 3 hours.
 19. The method of claim 18, wherein the oven is filled with a mixture of N₂ and H₂. 